Marine-Lenhart syndrome: a comprehensive literature review on diagnosis and management with emphasis on nuclear medicine approach

Marine-Lenhart syndrome (MLS) is a rare variant of hyperthyroidism characterized by the coexistence of Graves' disease and autonomously functioning thyroid nodules. This comprehensive literature review aims to synthesize current knowledge regarding the pathophysiology, diagnostic approach, and management of MLS, with a particular focus on the role of nuclear medicine. A structured review of relevant literature-including clinical studies, case reports, and international guidelines-was conducted to explore thyroid anatomy, mechanisms of nodule formation, imaging findings, and therapeutic strategies. Thyroid scintigraphy using radiotracers such as 99m Tc-pertechnetate remains central to the diagnosis of MLS, enabling functional distinction between diffusely hyperactive tissue and coexisting nodules. Despite advances in ultrasonography and fine-needle aspiration biopsy, nuclear imaging continues to offer unique functional insights. Treatment typically involves antithyroid drugs and radioiodine (¹³¹I) therapy; however, higher radioiodine doses may be necessary due to the relative resistance of autonomously functioning nodules. Newer imaging modalities, such as ¹⁸F-fluorodeoxyglucose PET/computed tomography (CT), are not useful for primary nodule characterization but may detect incidental fluorodeoxyglucose-avid nodules that warrant further evaluation. MLS poses a diagnostic challenge due to its overlapping features with other thyroid disorders and the potential for malignancy within cold nodules. This review highlights the indispensable role of nuclear medicine in diagnosing and tailoring treatment for MLS, ultimately promoting better outcomes through precise functional assessment.